libpng is a library for reading and writing PNG (Portable Network Graphics) image files. It provides a powerful API for performing various operations on PNG images. In this blog post, we will explore some of the key functions and features of the libpng API.

Contents

1. Reading a PNG File
2. Writing a PNG File
3. Handling Errors

Reading a PNG File

To read a PNG file using libpng, you can use the png_create_read_struct and png_create_info_struct functions to initialize the required data structures. Once the structures are initialized, you can use the png_init_io function to associate the input file pointer with the PNG read structure. Finally, you can use the png_read_png function to read the PNG image data.

png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (!png_ptr) {
    // Error handling
}
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr) {
    // Error handling
}
png_init_io(png_ptr, input_file);
png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);

Writing a PNG File

To write a PNG file using libpng, you can use the png_create_write_struct and png_create_info_struct functions to initialize the required data structures. Once the structures are initialized, you can use the png_init_io function to associate the output file pointer with the PNG write structure. Finally, you can use the png_write_png function to write the PNG image data.

png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (!png_ptr) {
    // Error handling
}
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr) {
    // Error handling
}
png_init_io(png_ptr, output_file);
png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);

Handling Errors

libpng provides error handling through a user-defined error function. You can set a custom error function using the png_set_error_fn function. This allows you to handle errors in a way that best fits your application’s needs.

void error_fn(png_structp png_ptr, png_const_charp error_msg) {
    // Custom error handling
}
png_set_error_fn(png_ptr, NULL, error_fn, NULL);

These are just a few examples of the functions and features provided by the libpng API. For more detailed information, please refer to the official libpng documentation.

By leveraging the libpng API, you can efficiently read and write PNG images in your C or C++ applications, providing a reliable and versatile solution for working with PNG files.